1. Field of the Invention
The present invention relates generally to a communication system where a plurality of communication apparatuses are connected to a plurality of communication lines respectively, in particular, to a relay apparatus making a communication apparatus detect an operation status of another communication apparatus connected to another communication line and controlling the communication apparatus in accordance with the operation status of another communication apparatus; communication system including the relay apparatus; and a communication method with using the relay apparatus.
2. Description of Related Art
It is recently known in several fields to utilize a system having many communication apparatuses, in which each communication apparatus is provided a certain function and connected with other communication apparatuses in order to perform variable operations through data exchange between many communication apparatuses. For example, it is known in a field of local area network (LAN) adapting for car to utilize electronic control units (ECUs) as the communication apparatuses, to make each ECU perform a certain operation and to exchange data between the ECUs, in order to provide various functions to be implemented by a system.
A number and a type are increased of the communication apparatuses connected to a communication medium in a system, proportionally to a specializing degree of the function provided to each communication apparatus, as well as an increasing degree of the functions performed by the system. Furthermore, the system is expected to perform much more various functions. Thus, each communication apparatus is required to share data and to interact with other communication apparatuses. Then, it results in an increase of exchanged data amount.
To accommodate the increase of exchanged data amount, communication apparatuses of the system is generally divided into some groups, and then each group is connected to a communication medium. This configuration can reduce communication traffic volume because of reducing the number of communication apparatuses connected to the communication medium. Thus, this configuration can prevent data collision and the like. Furthermore, it is thought to focus on data type treated by the groups of communication apparatus, and then to connect each group to each of communication mediums respectively having different communication speed. In such a configuration, a group treating a predetermined data type is connected with another group treating another predetermined data type, by a gateway apparatus that controls data transmission.
Japanese Patent Application Laid-Open No. 2005-159568 discloses that: ECUs in a field of LAN adapting for car are divided into some groups; each group is connected to each of communication lines of car; the communication lines of car are connected to each other by a gateway apparatus; priority information is added to the received and transmitted data to recognize data priority; the data priority is recognized through the priority information and the data having high priority is preferentially transmitted when the gateway apparatus performs data transmission between different communication lines of car, to prevent a transmission delay of data having high priority even when the communication lines of car take increased duty for data transmission.